Recently, mobile communication schemes based on orthogonal frequency division multiplexing (OFDM) have been investigated. Mobile communication schemes based on a combination of OFDM and communication technology using another communication scheme have also been investigated. The other communication scheme may be, for example, code division multiplexing access (CDMA).
The next generation specification is being investigated as long term evolution (LTE) even in the 3rd Generation Partnership Project (3GPP) that performs standardization of mobile phones. Further, 3GPP employs OFDM as a downlink communication scheme.
In the downlink communication scheme that is being investigated as the LTE, a reference signal (RS) equivalent to a known symbol (also referred to as a pilot symbol) is transmitted from a transmitter to a receiver via each antenna. There are three reference signals (1) to (3) shown below.
(1) Cell-specific reference signals
(2) MBSFN reference signals
(3) UE-specific reference signals
Non-Patent Document 1 discloses which of the reference signals (1) to (3) is arranged in which symbol. In addition, Non-Patent Documents 2 and 3 disclose associated technology.
Setting an arrangement of the cell-specific reference signals in each base station device, which is a transmitter, is under investigation. Arrangement of the cell-specific reference signals is disclosed in Non-Patent Document 1.
For arrangement of reference signals, there are two schemes: shifting and hopping.
In the shifting scheme, the reference signals are arranged by shifting an RS basic pattern in a frequency direction in a specific pattern corresponding to a cell ID unique to a cell. In the shifting scheme, the arrangement of the RS basic pattern is not changed in a time direction (subframe unit).
Meanwhile, in the hopping scheme, the reference signals are arranged by shifting an RS basic pattern in a frequency direction in a specific pattern corresponding to a cell ID unique to a cell. In the hopping scheme, the shift in the frequency direction according to the specific pattern corresponding to the cell ID specific to the cell is continuously performed even in a time direction.
In the related art, when hopping is performed with no limit, the complexity in channel estimation increases. Inversely, when shifting is performed, the complexity in the channel estimation is small, but the throughput characteristic is deteriorated. Further, when the RS arrangement disclosed in Non-Patent Document 2 is used, the precision of the channel estimation is deteriorated.
Therefore, in the related art, there are problems in that a channel estimation process in a receiver with respect to a signal transmitted from a transmitter becomes complicated, and the throughput in communication between the transmitter and the receiver is reduced.    Non-Patent Document 1: 3GPP TS 36.211 Technical Specification Group Radio Access Network; Physical Channels and Modulation V8.0.0    Non-Patent Document 2: Marvell Semiconductors, “Complexity and performance of channel estimation with hopping RS” (3GPP R1-071759)    Non-Patent Document 3: Qualcomm Europe, “Details on hopping of DL RS” (3GPP R1-072027)